Stably operable image-forming apparatus with improved paper conveying and ejecting mechanism

TECHNICAL FIELD

The present invention relates generally to image-forming apparatuses, and more particularly to an image-forming apparatus that uses a conveyor belt to convey a sheet of paper.

BACKGROUND ART

An ink-jet printer is a well-known one of image-forming apparatuses (or image-recording apparatuses) such as printers, facsimile machines, and copiers. The ink-jet printer performs recording on a recording medium such as paper (recording paper) by ejecting ink from a recording head. The recording medium is not limited to paper. The recording medium refers to a medium on which an image is formable. The recording medium may be an OHP (overhead projector) sheet, for instance. The ink-jet printer can record a high-definition image at high speed with low running cost and reduced noise. Further, the ink-jet printer enjoys another advantage of easiness in recording a color image using multiple color inks.

A well-known ink-jet head includes, as a part for generating energy to eject ink, a piezoelectric actuator such as a piezoelectric element, a thermal actuator, a shape memory alloy actuator, or an electrostatic actuator. The thermal actuator utilizes the phase change of liquid caused by film boiling using an electrothermal transducer such as a heat element. The shape memory alloy actuator utilizes the phase change of metal caused by a change in temperature. The electrostatic actuator employs an electrostatic force.

There is an image-forming apparatus of an electrophotographic type. This type of image-forming apparatus forms a toner image on a photosensitive body using a charging unit, an exposure unit, and a developing unit provided around a photosensitive body drum, transfers the toner image to paper by a transfer unit, and fixes the toner image on the paper by a fixing unit.

Paper conveying units for such an image-forming apparatus are provided. Japanese Laid-Open Patent Application No. 7-53082 (Prior Art 1) discloses a paper conveying unit that conveys a sheet of paper fed at an angle from above directly in a horizontal direction and ejects the sheet of paper after recording. Meanwhile, Japanese Laid-Open Patent Application No. 8-295438 (Prior Art 2) discloses a paper conveying unit that changes the conveying direction of a sheet of paper fed substantially vertically from below by substantially 90 degrees using a guide member having a section with a round profile, and ejects the sheet of paper after recording.

Two types of conveyors may be used for conveying a sheet of paper. The first type of conveyor employs conveying rollers to convey a sheet of paper. Meanwhile, Prior Art 1 and Prior Art 2 disclose the second type of conveyor with an endless charged belt. The second type of conveyor causes a sheet of paper to adhere electrostatically to the charged surface of the charged belt, and rotates the charged belt with the sheet of paper adhering thereto so as to convey the sheet of paper. Thereby, this type of conveyor prevents the sheet of paper from being detached from the charged belt, thus maintaining a high flatness of the sheet of paper.

The image-forming apparatus of Prior Art 2 horizontally conveys the sheet of paper fed substantially vertically from below by changing the conveying direction of the sheet of paper by substantially 90 degrees by causing the fed sheet of paper to come into contact with a conveying guide formed along the surface of the conveyor belt (or a conveying path with a round profile).

In the case of horizontally conveying a sheet of paper fed substantially vertically in an upward direction by changing the conveying direction of the sheet of paper by substantially 90 degrees while guiding the sheet of paper by a conveying guide in a conveying path having a section with a round profile as in the image-forming apparatus of Prior Art 2, if the sheet of paper is plain paper, the resistance generated at the conveying guide is low when the sheet of paper comes into contact with the conveying guide. As a result, the sheet of paper can be conveyed with high accuracy without any problem even with a conveying belt with a low coefficient of friction μ.

On the other hand, thick paper such as glossy paper for improving image quality or a card is used particularly in an ink-jet recording apparatus. If such thick paper is used, the resistance generated at the time of changing the conveying direction of the sheet of paper becomes high so that the generated resistance exceeds conveying power if a conveyor belt with a low coefficient of friction μ is employed. This results in the phenomenon that the sheet of paper slips on the conveyor belt.

Thus, if a conveyor belt with a low coefficient of friction μ, which is prevented from generating large conveying power, is employed in conveying a sheet of paper that requires large conveying power, the conveyance of the sheet of paper becomes unstable so that a paper jam is more likely to occur.

According to ink-jet recording, ink adheres to paper. Therefore, when an image is formed on the paper, moisture included in the ink causes the paper to stretch. This phenomenon is referred to as cockling. Cockling causes paper waviness so that the distance between a nozzle of a recording head and a paper surface varies depending on a position on the paper surface. Cockling may worsen to such an extent that, in the worst case, the paper comes into contact with the nozzle surface of the recording head. As a result, not only the nozzle surface of the recording head but also the paper itself may be contaminated so that image quality is degraded. Further, ink droplet misdirection may be caused by the effect of cockling.

According to a conventional ink-jet recording apparatus, paper feeding is performed by rollers. A pair of rollers is provided on each side of an image printing region (where a recording head performs printing) in a paper feed direction. One of the pairs is the combination of a spur and a roller. According to this configuration, however, the accuracy of paper feeding can be guaranteed only when paper is held between each pair of rollers.

Due to a recent demand for an increase in the printing region, however, some ink-jet printing apparatuses perform printing with paper being held by only one of the two pairs of rollers, which is a state that cannot guarantee the accuracy of paper feeding, in order to secure the printing region. With paper being held by only one of the two pairs of rollers, however, the occurrence of paper flotation cannot be handled or the accuracy of paper feeding cannot be guaranteed because of insufficient conveying power. This results in the degradation of image quality.

Therefore, an ink-jet recording apparatus that includes an endless charged belt to maintain the flatness of paper has been proposed. Such an ink-jet recording apparatus causes paper to adhere electrostatically to the charged surface of the charged belt, and rotates the charged belt with the paper adhering thereto so as to convey the paper. Thereby, the ink-jet recording apparatus prevents the paper from being detached from the charged belt, thus maintaining a high flatness of the paper. Such an ink-jet recording apparatus is disclosed in Japanese Patent No. 2897960 (Prior Art 3) and Japanese Laid-Open Patent Application No. 7-53081 (Prior Art 4).

In the case of conveying paper electrostatically adhering to a conveyor belt as in the above-described conventional ink-jet recording apparatus, the flatness of the paper is directly linked to the flatness of the conveyor belt.

In this case, the conveyor belt engages at least two rollers to extend therebetween so that a chord part of the conveyor belt opposes an image printing region. However, the conveyor belt is prone to have wrinkles in its chord part, and when the conveyor belt is rotated, the conveyor belt may undulate in its chord part. As a result, the flatness of the conveyor belt may decrease.

Thus, even in the case of employing a conveyor belt, a decrease in the flatness of the conveyor belt causes a variation in the distance between a recording head and paper, thus degrading image quality.

Further, in the case of conveying paper electrostatically adhering to a conveyor belt as in the above-described conventional ink-jet recording apparatus, in order to stack the paper in a paper ejection part, the paper is separated from the conveyor belt by self stripping. Inelastic paper or paper that has lost elasticity with a solid image formed thereon, however, is prevented from being separated from the conveyor belt by self stripping, and remains adhered to the conveyor belt. As a result, a paper jam occurs.

Furthermore, in the case of conveying paper electrostatically adhering to a conveyor belt as in the above-described conventional ink-jet recording apparatus, it is necessary to secure an electrostatic adhesive force by the conveyor belt to cause the paper to adhere to the conveyor belt. In the conventional image-forming apparatus, however, the conveyor belt is a single-layer belt so that a sufficient electrostatic adhesive force to convey the paper stably cannot be obtained.

SUMMARY

In an aspect of this disclosure, an image-forming apparatus is provided that can stably convey paper that requires a large conveying power by changing the conveying direction of the paper.

In another aspect of this disclosure, an image-forming apparatus is provided that can maintain the flatness of a conveyor belt and perform recording with high image quality.

In another aspect of this disclosure, an image-forming apparatus is provided that can ensure the separation of paper from a conveyor belt.

In another aspect of this disclosure, an image-forming apparatus is provided that can stably convey paper using a conveyor belt.

In an exemplary embodiment of this disclosure, an image-forming apparatus includes an endless conveyor belt rotatable to convey paper with a surface of the conveyor belt being charged, a counter roller for holding the paper between the conveyor belt and the counter roller and conveying the paper, and a clutch part that is caused to slip by a difference in velocity between the conveyor belt and the counter roller, wherein the counter roller is driven through the clutch part.

In another exemplary embodiment of this disclosure, an image-forming apparatus includes a conveying roller rotatable to convey paper, a counter roller for holding the paper between the conveying roller and the counter roller and conveying the paper, and a clutch part that is caused to slip by a difference in velocity between the conveying roller and the counter roller, wherein the counter roller is driven through the clutch part.

According to the above-described image-forming apparatuses, the counter roller for holding the paper between the conveyor belt or the conveying roller and the counter roller and conveying the fed paper is driven through the clutch part caused to slip by the difference in velocity between the counter roller and the conveyor belt or the conveying roller. Accordingly, even paper requiring a large conveying power is stably conveyable, with its conveying direction being changed, without incurring frictional electrification that affects conveyability and images and an increase in load due to friction.

In another exemplary embodiment of this disclosure, an image-forming apparatus includes an endless conveyor belt rotatable to convey paper with a surface of the conveyor belt being charged, the conveyor belt being supported by at least two rollers, and engaging the two rollers so as to extend therebetween, a recording head ejecting a liquid droplet to record an image on the paper in a printing region, and a guide member provided on an inner side of the conveyor belt in a position corresponding to the printing region with a surface of the guide member projecting toward the recording head beyond a tangent of the rollers supporting the conveyor belt, the surface of the guide member coming into contact with the conveyor belt.

According to the above-described image-forming apparatus, the chord part of the conveyor belt which part corresponds to the printing region can be prevented from including waviness or a variation in movement. As a result, it is possible to record an image with high quality.

In another exemplary embodiment of this disclosure, an image-forming apparatus includes an endless conveyor belt rotatable to convey paper with a surface of the conveyor belt being charged and the paper adhering to the surface, the conveyor belt being supported by at least two rollers, and engaging the two rollers so as to extend therebetween, a recording head ejecting a liquid droplet to record an image on the paper, and a separation mechanism that separates the paper from the conveyor belt on a side of the conveyor belt on which side the paper on which the image is recorded is ejected from the image-forming apparatus.

According to the above-described image-forming apparatus, the separation mechanism is provided on the paper ejection side of the conveyor belt. Accordingly, it is ensured that the paper is separated from the conveyor belt and ejected, thus preventing the occurrence of a paper jam.

In another exemplary embodiment of this disclosure, an image-forming apparatus includes an endless conveyor belt rotatable to convey paper with a surface of the conveyor belt being charged and the paper adhering to the surface, the conveyor belt being supported by at least two rollers, and engaging the two rollers so as to extend therebetween, and a recording head ejecting a liquid droplet to record an image on the paper, the paper being ejected from the image-forming apparatus after the image is recorded on the paper, wherein the conveyor belt includes a double-layer structure including an insulating layer and a medium resistance layer.

According to the above-described image-forming apparatus, the conveyor belt is formed of a double-layer structure including a top (outer) layer, which is the insulating layer, and a bottom (inner) layer, which is the medium resistance layer. Accordingly, a sufficient electrostatic adhesive force can be obtained so that the paper can be conveyed stably and thus image quality can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a diagram showing a configuration of an ink-jet recording apparatus as an image-forming apparatus according to a first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> is a plan view of part of the ink-jet recording apparatus according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 3</figref> is a diagram showing part of a conveying part of the ink-jet recording apparatus according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 4</figref> is a diagram for illustrating a structure of a conveyor belt of the ink-jet recording apparatus according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 5</figref> is a diagram for illustrating an arrangement of a guide member of the ink-jet recording apparatus according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 6</figref> is a perspective view of the guide member according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 7</figref> is a diagram for illustrating a drive system of a counter roller of the ink-jet recording apparatus according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 8</figref> is another diagram for illustrating the drive system of the counter roller of the ink-jet recording apparatus according to the first embodiment of the present invention; and

<figref idref="DRAWINGS">FIG. 9</figref> is a diagram for illustrating a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A description is given below, with reference to the accompanying drawings, of embodiments of the present invention.

First Embodiment

A description is given of a first embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 1</figref> is a diagram showing a configuration of an ink-jet recording apparatus as an image-forming apparatus according to the first embodiment of the present invention. <figref idref="DRAWINGS">FIG. 2</figref> is a plan view of part of the ink-jet recording apparatus. <figref idref="DRAWINGS">FIG. 3</figref> is a diagram showing part of a conveying part of the ink-jet recording apparatus.

Referring to <figref idref="DRAWINGS">FIGS. 1 and 2</figref>, the ink-jet recording apparatus of the present invention includes a guide rod <b>1</b> and a stay <b>2</b> provided as guide members extending between side plates (not shown in the drawings) on the X₁and X₂sides. The ink-jet recording apparatus holds a carriage <b>3</b> by the guide rod <b>1</b> and the stay <b>2</b> so that the carriage <b>3</b> is slidable in a main scanning direction or the X₁and X₂directions. A main scanning motor (not shown in the drawings) drives the carriage <b>3</b> so that the carriage <b>3</b> moves and scans in the X₁and X₂directions.

The carriage <b>3</b> includes a recording head <b>4</b> composed of four ink-jet heads of yellow (Y), cyan (C), magenta (M), and black (Bk) ejecting ink droplets of respective colors. The recording head <b>4</b> is attached so that the ink ejection openings of the recording head <b>4</b> are arranged in a direction to cross the main scanning direction and ink is ejected from the ink ejection openings in the Z₂(downward) direction.

Each ink-jet head composing the recording head <b>4</b> may employ a piezoelectric actuator such as a piezoelectric element, a thermal actuator, a shape memory alloy actuator, or an electrostatic actuator as a part for generating energy to eject ink.

The carriage <b>3</b> includes sub tanks <b>5</b> of the four colors for supplying the respective color inks to the recording head <b>4</b>. The color inks are supplied from respective main tanks (ink cartridges) through ink supply tubes (not shown in the drawings) to the corresponding sub tanks <b>5</b>.

Further, the ink-jet recording apparatus includes a paper feed part for feeding sheets of paper <b>12</b> stacked on a paper stacking part (a pressure plate) <b>11</b> of a paper feed cassette <b>10</b>. The paper feed part includes a crescent-shaped roller (a paper feed roller) <b>13</b> that separates and feeds the sheets of paper <b>12</b> one by one from the paper stacking part <b>11</b> and a separation pad <b>14</b> formed of a material with a high coefficient of friction and provided to oppose the paper feed roller <b>13</b>. The separation pad <b>14</b> is biased toward the paper feed roller <b>13</b>.

The ink-jet recording apparatus includes a conveying part for conveying each sheet of paper <b>12</b> fed from the paper feed part below (on the Z₂side of) the recording head <b>4</b>. The conveying part includes a conveyor belt <b>21</b>, a counter roller (a pressure roller) <b>22</b>, a conveying guide <b>23</b>, an edge pressure roller <b>25</b>, and a charging roller <b>26</b>. The conveyor belt <b>21</b> conveys the sheet of paper <b>12</b> by causing the sheet of paper <b>12</b> to adhere electrostatically to the conveyor belt <b>21</b>. A sheet of paper <b>12</b> is fed through a guide <b>15</b> from the paper feed part to be conveyed and held between the conveyor belt <b>21</b> and the counter roller <b>22</b>. The conveying guide <b>23</b> changes the conveying direction of the sheet of paper <b>12</b> fed substantially vertically in the upward (Z₁) direction by substantially 90 degrees so that the sheet of paper <b>12</b> is conveyed on and along the conveyor belt <b>21</b>. The edge pressure roller <b>25</b> is biased toward the conveyor belt <b>21</b> by a holding member <b>24</b>. The charging roller <b>26</b> is a charging part that charges the surface of the conveyor belt <b>21</b>. A holding roller <b>30</b> is provided to the Y₂end of the holding member <b>24</b>. The holding roller <b>30</b> may be omitted from the ink-jet recording apparatus.

Referring to <figref idref="DRAWINGS">FIGS. 1 and 3</figref>, the conveyor belt <b>21</b> is an endless belt (a belt with no ends or a belt whose both ends are connected), and engages a conveying roller <b>27</b> and a tension roller <b>28</b> provided with tension so as to extend therebetween. The conveyor belt <b>21</b> rotates in the direction indicated by arrow A in <figref idref="DRAWINGS">FIG. 3</figref>. This direction may be referred to as a belt or paper conveying direction.

Referring to <figref idref="DRAWINGS">FIG. 4</figref>, the conveyor belt <b>21</b> includes a top (outer) layer <b>21</b><i>a </i>and a bottom (inner) layer <b>21</b><i>b</i>. The top layer <b>21</b><i>a </i>serves as a paper adhesion surface to which a sheet of paper <b>12</b> may adhere. The top layer <b>21</b><i>a </i>is formed of an approximately 40 μm-thick pure resin material, for instance, a pure ETFE (Ethylene Tetra Fluoro Ethylene) material, with no resistance control. The bottom layer <b>21</b><i>b </i>is formed of the same material as the top layer <b>21</b><i>a</i>, to which resistance control by carbon is provided. The bottom layer <b>21</b><i>b </i>may also be referred to as a medium resistance layer or a ground layer.

The thickness of the insulating layer (top layer) <b>21</b><i>a </i>of the conveyor belt <b>21</b> affects a dielectric constant. If the thickness becomes greater, the dielectric constant becomes lower so that the amount of electric charge on the conveyor belt <b>21</b> at the time of the charging of the conveyor belt <b>21</b> decreases. Accordingly, the electrostatic adhesive force can be increased by making the top layer <b>21</b><i>a </i>as thin as possible within a range where the thickness of the top layer <b>21</b><i>a </i>is prevented from becoming zero even if the conveyor belt <b>21</b> is damaged by actual use. Further, the range of variation of the layer thickness, which may vary for manufacturing reasons, should also be considered in making the top layer <b>21</b><i>a </i>as thin as possible. According to experiments, a desired electrostatic adhesive force was obtained with the thickness of the top layer <b>21</b><i>a </i>being less than or equal to 60 μm.

The thickness of the bottom layer <b>21</b><i>b </i>of the conveyor belt <b>21</b> does not directly affect the electrostatic action. If the total thickness of the conveyor belt <b>21</b> increases, however, its rigidity increases so that it becomes difficult to secure the flatness of the conveyor belt <b>21</b> when the conveyor belt <b>21</b> is mounted (tightened) in an actual apparatus. On the other hand, the thickness of the conveyor belt <b>21</b> cannot be overly reduced in order to secure required strength. According to experiments, it is desired that the bottom layer <b>21</b><i>b </i>be approximately 40 to 200 μm in thickness, and more preferably, approximately 50 to 200 μm in thickness.

Thus, the conveyor belt <b>21</b> is formed to have a double-layer structure with the layer <b>21</b><i>b </i>with resistance control being formed on the bottom (inner) surface of the conveyor belt <b>21</b>. This structure makes it possible to previously form an electric charge on the top layer <b>21</b><i>a</i>, which is an insulating layer, and thereafter supply an additional electric charge to the top layer <b>21</b><i>a </i>when the sheet of paper <b>12</b> that is to adhere to the conveyor belt <b>21</b> comes into contact therewith, thereby increasing the electrostatic adhesive force between the sheet of paper <b>12</b> and the conveyor belt <b>21</b>. If the conveyor belt <b>12</b> is formed of only a single insulating layer, the adhesive force is reduced by half compared with the above-described case of the double-layer structure. Further, in the case of the single-layer structure, the sheet of paper <b>12</b> should start to come into contact with the conveyor belt <b>21</b> at a position opposite a ground roller provided inside the conveyor belt <b>21</b>. No such restriction is imposed in the case of the double-layer structure.

In this case, a desired electrostatic adhesive force was obtained using a material with a surface resistivity of 1E+10 Ω/sq. or more as the top layer <b>21</b><i>a </i>and a material with a surface resistivity of 1E+08 Ω/sq. or less as the bottom layer <b>21</b><i>b. </i>

The charging roller <b>26</b> is disposed so as to come into contact with the top layer <b>21</b><i>a </i>of the conveyor belt <b>21</b> and rotate, driven by the rotation of the conveyor belt <b>21</b>. A force of 2.5 N is applied to each end of the shaft of the charging roller <b>26</b> as pressure. The conveying roller <b>27</b>, which also serves as the above-described ground roller, is disposed in contact with the medium resistance layer (bottom layer) <b>21</b><i>b </i>of the conveyor belt <b>21</b> to be grounded. The conveying roller <b>27</b> may have a volume resistivity of 1E+10 Ω·cm or less so as to also serve as a ground roller.

Referring to <figref idref="DRAWINGS">FIGS. 3 and 5</figref>, on the bottom-layer (inner) side of the conveyor belt <b>21</b>, a guide member <b>31</b> is provided at a position corresponding to a printing region where the recording head <b>4</b> performs printing. Referring to <figref idref="DRAWINGS">FIGS. 3 and 6</figref>, the X₁and X₂ends of the guide member <b>31</b> are supported by frame members <b>35</b> holding the conveying roller <b>27</b> and the tension roller <b>28</b> so that the guide member <b>31</b> is held between the frame members <b>35</b>.

Referring to <figref idref="DRAWINGS">FIG. 5</figref>, an upper (Z₁-side) surface <b>31</b><i>a </i>of the guide member <b>31</b> projects toward the recording head <b>4</b> beyond a tangent <b>32</b> of the conveying roller <b>27</b> and the tension roller <b>28</b> supporting the conveyor belt <b>21</b>. According to this configuration, in the printing region, the conveyor belt <b>21</b> is guided, being pushed up by the upper surface of the guide member <b>31</b>, so as to maintain high flatness.

Thus, the guide member <b>31</b> provided on the bottom-layer side of the conveyor belt <b>21</b> pushes up the chord part of the conveyor belt <b>21</b> which part corresponds to the printing region toward the recording head <b>4</b> side so that the conveyor belt <b>21</b> moves along the guide member <b>31</b>. This prevents the occurrence of wrinkles or waviness in the chord part of the conveyor belt <b>21</b>. As a result, the flatness of the conveyor belt <b>21</b> can be kept high, so that recording can be performed with high image quality.

Further, referring to <figref idref="DRAWINGS">FIG. 6</figref>, on the surface <b>31</b><i>a </i>of the guide member <b>31</b>, which surface <b>31</b><i>a </i>comes into contact with the bottom (inner) surface of the conveyor belt <b>21</b>, a plurality of grooves <b>31</b><i>b </i>are formed in a direction perpendicular to the belt conveying direction in order to reduce the area of contact with the conveyor belt <b>21</b>. As a result, the conveyor belt <b>21</b> can move smoothly on and along the surface of the guide member <b>31</b>.

Further, referring to <figref idref="DRAWINGS">FIG. 3</figref>, a guide roller <b>33</b> and a guide roller <b>34</b> are rotatably provided in contact with the bottom surface of the conveyor belt <b>21</b> on the upstream side and the downstream side, respectively, of the guide member <b>31</b> in the belt conveying direction. It is preferable that the guide rollers <b>33</b> and <b>34</b> be disposed close to the Y₁and Y₂ends, respectively, of the guide member <b>31</b> in the belt conveying direction.

Thus, the guide rollers <b>33</b> and <b>34</b> are rotatably provided in contact with the bottom surface of the conveyor belt <b>21</b> on the upstream side and the downstream side, respectively, of the guide member <b>31</b> in the belt conveying direction. As a result, the friction generated between the conveyor belt <b>21</b> and the Y₁and Y₂ends of the guide member <b>31</b> can be reduced. Accordingly, a driving load by the conveyor belt <b>21</b> can be decreased, and a variation in the movement of the conveyor belt <b>21</b> due to the rubbing of the conveyor belt <b>21</b> against the ends of the guide member <b>31</b> can also be avoided. Accordingly, it is possible to prevent wrinkles or waviness from occurring in the chord part of the conveyor belt <b>21</b> with more certainty. As a result, the flatness of the conveyor belt <b>21</b> can be kept high, so that recording can be performed with high image quality.

The ink-jet recording apparatus includes a paper ejection part for ejecting each sheet of paper <b>12</b> on which the recording head <b>4</b> has performed recording. Referring to <figref idref="DRAWINGS">FIGS. 1 and 3</figref>, the paper ejection part includes a separation claw <b>41</b> serving as a separation mechanism for separating the sheet of paper <b>12</b> from the conveyor belt <b>21</b>, paper ejection rollers <b>42</b> and <b>43</b>, and a paper ejection tray <b>44</b> for stocking the ejected sheet of paper <b>12</b>. The separation claw <b>41</b> is provided in contact with the conveyor belt <b>21</b>. The paper ejection rollers <b>42</b> and <b>43</b> are provided on the downstream side of the separation claw <b>41</b> in the belt or paper conveying direction. The paper ejection tray <b>44</b> is provided on the downstream side of the paper ejection rollers <b>42</b> and <b>43</b>. The separation claw <b>41</b> is supported by a support shaft <b>41</b><i>a </i>so as to be pivotable. An elastic body <b>45</b> such as a spring applies tension to the separation claw <b>41</b> toward the conveyor belt <b>21</b> so that the separation claw <b>41</b> remains in contact with the surface of the conveyor belt <b>21</b>.

A duplex paper feed unit (a duplex printing mechanism) <b>51</b> for duplex printing (printing on both sides of the sheet of paper <b>12</b>) is attached to the main body of the ink-jet recording apparatus (on the rear or Y₁side) so as to be detachable therefrom and attachable thereto. The duplex paper feed unit <b>51</b> receives (captures) the sheet of paper <b>12</b> conveyed in the direction opposite to the belt conveying direction (in the Y₁direction in <figref idref="DRAWINGS">FIG. 1</figref>) by the reverse rotation of the conveying belt <b>21</b>. Then, the duplex paper feed unit <b>51</b> turns the received sheet of paper <b>12</b> upside down, and again feeds the turned sheet of paper <b>12</b> to the space between the counter roller <b>22</b> and the conveyor belt <b>21</b>.

A description is given, with reference to <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, of the drive system of the counter roller <b>22</b>.

According to the drive system of the counter roller <b>22</b>, the conveyor belt <b>21</b> is rotated by a sub scanning motor <b>61</b> rotating the conveying roller <b>27</b> through a timing belt <b>62</b> and a timing gear <b>63</b> attached to a shaft <b>27</b><i>a </i>of the conveying roller <b>27</b>.

Referring to <figref idref="DRAWINGS">FIG. 8</figref>, an intermediate gear <b>66</b> including a one-way clutch <b>65</b> is attached to the shaft <b>27</b><i>a </i>of the conveying roller <b>27</b>. The one-way clutch <b>65</b> is a clutch part that is caused to slip by the difference in velocity between the conveying roller <b>27</b> and the counter roller <b>22</b>. The intermediate gear <b>66</b> engages a driving gear <b>67</b> attached to a shaft <b>22</b><i>a </i>of the counter roller <b>22</b>. As a result, a rotational driving force is transmitted from the sub scanning motor <b>61</b> through the shaft <b>27</b><i>a </i>of the conveying roller <b>27</b>, the one-way clutch <b>65</b>, the intermediate gear <b>66</b>, and the driving gear <b>67</b> to the counter roller <b>22</b>.

In this case, the one-way clutch <b>65</b> transmits the rotation of the shaft <b>27</b><i>a </i>to the intermediate gear <b>66</b> when the conveying roller <b>27</b> rotates in the direction indicated by arrow A in <figref idref="DRAWINGS">FIGS. 7 and 8</figref> (also referred to as a forward conveying direction). The one-way clutch <b>65</b> does not transmit the rotation of the shaft <b>27</b><i>a </i>to the intermediate gear <b>66</b> when the conveying roller <b>27</b> rotates in the direction opposite to the forward conveying direction (or in the direction in which the sheet of paper <b>12</b> is fed into the duplex paper feed unit <b>51</b> for duplex printing).

According to the drive system of the counter roller <b>22</b>, the linear velocity of the counter roller <b>22</b> is set to be lower than the linear velocity of the conveyor belt <b>21</b>. The velocity ratio is set so that the linear velocity of the counter roller <b>22</b> is lower than the linear velocity of the conveyor belt <b>21</b> by approximately 2%. The experimental results showed that this velocity ratio was the most effective in this ink-jet recording apparatus.

According to the ink-jet recording apparatus having the above-described configuration, sheets of paper <b>12</b> are separated and fed one by one from the paper feed part, and each sheet of paper <b>12</b> is fed substantially vertically in the upward direction and is guided by the guide <b>15</b> to be conveyed and held between the conveyor belt <b>21</b> and the counter roller <b>22</b>, both of which are rotated, as shown in <figref idref="DRAWINGS">FIG. 7</figref>. Then, the fed sheet of paper <b>12</b> has its leading edge guided by the conveying guide <b>23</b> and pressed against the conveyor belt <b>21</b> by the edge pressure roller <b>25</b>. Thereby, the conveying direction of the sheet of paper <b>12</b> is changed by approximately 90 degrees.

At this point, both the conveyor belt <b>21</b> and the counter roller <b>22</b> are rotated by the rotational driving force received from the sub scanning motor <b>61</b>. Accordingly, even when the sheet of paper <b>12</b> is elastic paper such as glossy paper or thick paper so as to have a high coefficient of friction against the conveying guide <b>23</b> and a low coefficient of friction μ against the conveyor belt <b>21</b>, the sheet of paper <b>12</b> can be fed without a slip and the conveying direction thereof can be changed so that the sheet of paper <b>12</b> can be conveyed on the conveyor belt <b>21</b>.

In this case, if only the counter roller <b>22</b> is driven, a difference in velocity may occur between the counter roller <b>22</b> and the conveyor belt <b>21</b> due to factors such as a variation in the diameter, expansion due to temperature, and wear of the counter roller <b>22</b>. Such a difference in velocity causes frictional electrification of the sheet of paper <b>12</b>, an increase in load, and a difference in load torque between apparatuses.

The ink-jet recording apparatus according to the first embodiment of the present invention drives the counter roller <b>22</b> through the one-way clutch <b>65</b>. Accordingly, when the linear velocity of the conveyor belt <b>21</b> is higher than that of the counter roller <b>22</b>, it is possible to cause the counter roller <b>22</b> to slip (or to rotate following the rotation of the conveyor belt <b>21</b>).

According to the first embodiment of the present invention, since the linear velocity of the counter roller <b>22</b> is set to be lower than that of the conveyor belt <b>21</b> (by approximately 2% as previously described), the one-way clutch <b>65</b> of the drive system of the counter roller <b>22</b> is caused to slip by the difference in velocity. As a result, a minute variation in the linear velocity is absorbed so as to make the conveyor belt <b>21</b> and the counter roller <b>22</b> substantially equal in velocity. This makes it possible to reduce frictional electrification of the sheet of paper <b>12</b>, to reduce load, and to reduce the difference in load torque between apparatuses.

On the other hand, if the linear velocity of the conveyor belt <b>21</b> is set to be lower than that of the counter roller <b>22</b>, a load on the drive system of the conveyor belt <b>21</b> increases to cause a difference in load torque between apparatuses.

In the case of duplex printing, the conveyor belt <b>21</b> is rotated in the direction opposite to the direction indicated by arrow A in <figref idref="DRAWINGS">FIG. 8</figref>. At this time, the one-way clutch <b>65</b> prevents a driving force from being transmitted to the counter roller <b>22</b> so that the counter roller <b>22</b> rotates following the rotation of the conveyor belt <b>21</b>. After the feeding of the sheet of paper <b>12</b> into the duplex paper feed unit <b>51</b> is completed, the conveyor belt <b>21</b> rotates again in the direction of arrow A in <figref idref="DRAWINGS">FIG. 8</figref> and operates in the same way as described above with respect to the sheet of paper <b>12</b> fed from the duplex paper feed unit <b>51</b>.

Thus, the sheet of paper <b>12</b> is fed on the conveyor belt <b>21</b> as previously described. At this time, a control circuit (not graphically represented) causes a high-voltage power supply to alternately apply a positive output and a negative output, or repeat application of alternate voltages, to the charging roller <b>26</b>. Accordingly, a pattern of the alternate charging voltages is formed on the conveyor belt <b>21</b>. That is, the conveyor belt <b>21</b> is alternately charged positively and negatively at predetermined intervals in the sub scanning direction in which the conveyor belt <b>21</b> rotates so that positively and negatively charged strip-shaped areas are successively formed. When the sheet of paper <b>12</b> is fed on the conveyor belt alternately charged positively and negatively, polarization to electric charges opposite to the charging pattern of the conveyor belt <b>21</b> occurs in the sheet of paper <b>12</b>. This is equivalent to the formation of capacitors connected in parallel. As a result, the sheet of paper <b>12</b> adheres to the conveyor belt <b>21</b> so that the conveyor belt <b>21</b> rotates to convey the sheet of paper <b>12</b> in the sub scanning direction.

Then, by driving the recording head <b>4</b> in accordance with an image signal while moving the carriage <b>3</b>, ink droplets are ejected on the sheet of paper <b>12</b> in a stationary state so as to perform recording for a line. After conveying the sheet of paper <b>12</b> a predetermined distance, recording is performed for the next line. When a recording end signal or a signal indicating that the trailing edge of the sheet of paper <b>12</b> has reached the recording region is received, the recording operation ends and the sheet of paper <b>12</b> is ejected onto the paper ejection tray <b>44</b>.

At this point, the paper ejection side (Y₂side) of the conveyor belt <b>21</b> faces the separation claw <b>41</b> so as to ensure the separation and ejection of the sheet of paper <b>12</b> from the conveyor belt <b>21</b> while the electrostatic adhesive force is increased by the above-described double-layer structure of the conveyor belt <b>21</b>. As a result, the sheet of paper is prevented from adhering to and thus being further conveyed by the conveyor belt <b>21</b>, thus avoiding a paper jam.

The counter roller <b>22</b> and its drive system according to the present invention are also applicable to an ink-jet recording apparatus that conveys a sheet of paper only with a conveying roller without using a conveyor belt.

Second Embodiment

Next, a description is given of a second embodiment of the present invention. The same elements as those of the first embodiment are referred to by the same numerals.

Referring to <figref idref="DRAWINGS">FIG. 9</figref>, the separation claw <b>41</b> is supported pivotably by the support shaft <b>41</b><i>a </i>so as to be contactable with (be able to come into contact with) and separable from the surface of the conveyor belt <b>21</b>. In the second embodiment, a plunger <b>61</b> for causing the separation claw <b>41</b> to come into contact with and separate from the surface of the conveyor belt <b>21</b> is provided instead of the elastic body <b>45</b>. A main control part <b>63</b> drives and controls the plunger <b>61</b> through a driver <b>64</b> based on a detection signal supplied from an edge detection sensor <b>62</b> detecting the edge (leading edge) of the sheet of paper <b>12</b>. The edge detection sensor <b>62</b> is provided to the carriage <b>3</b>.

According to this configuration, the plunger <b>61</b> may be driven to cause the separation claw <b>41</b> to come into contact with the surface of the conveyor belt <b>21</b> so as to separate the sheet of paper <b>12</b> therefrom at the time of performing recording on and ejecting the sheet of paper <b>12</b> (that is, for a period of time required for the leading edge of the sheet of paper <b>12</b> to reach the paper ejection part after being detected by the edge detection sensor <b>62</b>). After the sheet of paper <b>12</b> is separated from the conveyor belt <b>21</b>, it is possible to end the driving of the plunger <b>61</b> to separate the separation claw <b>41</b> from the surface of the conveyor belt <b>21</b>.

According to this configuration, it is possible to cause the separation claw <b>41</b> to come into contact with the surface of the conveyor belt <b>21</b> only when required. Accordingly, the durability of the conveyor belt <b>21</b> is improved.

According to the present invention, the ink-jet recording apparatus (image-forming apparatus) includes the counter roller <b>22</b> for holding the sheet of paper <b>12</b> between the conveyor belt <b>21</b> or the conveying roller <b>27</b> and the counter roller <b>22</b> and conveying the fed sheet of paper <b>12</b>. The counter roller <b>22</b> is driven through the one-way clutch (clutch part) <b>65</b> caused to slip by the difference in velocity between the counter roller <b>22</b> and the conveyor belt <b>21</b> or the conveying roller <b>27</b>. Accordingly, even paper requiring a large conveying power is stably conveyable, with its conveying direction being changed, without incurring frictional electrification that affects conveyability and images and an increase in load due to friction.

Further, the conveyor belt <b>21</b> for conveying the sheet of paper <b>12</b> is supported by and engages at least the two rollers <b>27</b> and <b>28</b>, and extends between the rollers <b>27</b> and <b>28</b>. The guide member <b>31</b> is provided on the bottom-layer side of the conveyor belt <b>21</b> in a position corresponding to the printing region where the recording head <b>4</b> performs recording. The upper surface <b>31</b><i>a </i>of the guide member <b>31</b> projects toward the recording head <b>4</b> side beyond the tangent <b>32</b> of the two rollers <b>27</b> and <b>28</b> supporting the conveyor belt <b>21</b>. This can prevent the chord part of the conveyor belt <b>21</b> corresponding to the printing region from including waviness or a variation in movement. As a result, it is possible to record an image with high quality.

Further, the separation mechanism (separation claw <b>41</b>) separating the sheet of paper <b>12</b> from the conveyor belt <b>21</b> is provided on the paper ejection side of the conveyor belt <b>21</b>. Accordingly, it is ensured that the sheet of paper <b>12</b> is separated from the conveyor belt <b>21</b> and ejected, thus preventing the occurrence of a paper jam.

Further, the conveyor belt <b>21</b> is formed of a double-layer structure including the top layer <b>21</b><i>a</i>, which is an insulating layer, and the bottom layer <b>21</b><i>b</i>, which is a medium resistance layer. Accordingly, a sufficient electrostatic adhesive force can be obtained so that the sheet of paper <b>12</b> can be conveyed stably and thus image quality can be improved.

In the above-described embodiments, the separation claw <b>41</b> is employed as a separation mechanism. Alternatively, an air separation mechanism that separates paper from the conveyor belt <b>21</b> by air blowing is also employable. Further, in the above-described embodiments, the ink-jet recording apparatus is a serial-type (shuttle-type) ink-jet recording apparatus where a carriage performs scanning. The present invention, however, is also applicable to a line-type ink-jet recording apparatus having a line-type head.

In addition to an ink-jet printer, the image-forming apparatus according to the present invention is also applicable to a facsimile machine, a copier, and a multi-function apparatus including the functions of a printer, a facsimile machine, and a copier. Further, the image-forming apparatus according to the present invention is also applicable to an image-forming apparatus that ejects liquid other than ink, such as a resist or a DNA sample in the medical field. Further, in terms of a recording method, the image-forming apparatus according to the present invention is applicable to not only an ink-jet recording apparatus but also an electrophotographic recording apparatus.

The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.

The present application is based on Japanese priority applications No. 2002-341834, filed on Nov. 26, 2002, No. 2002-341944, filed on Nov. 26, 2002, No. 2002-342036, filed on Nov. 26, 2002, and No. 2003-023221, filed on Jan. 31, 2003, the entire contents of which are hereby incorporated by reference.